One aspect to this question is the time frame of availability. Hog, Deep6 and Poseidon have a business model that serves tech divers very well (they sell parts and offer courses), and at the moment they would likely be your solution. But big companies are likely to have parts made and stocked for decades (which by now has become EU law). If the reg is well priced and you dive a lot, you'd replace it anyway though.
If you add "anywhere in the world" to your question, then things change. If you break a rare part somewhere remote, Scubapro and Aqualung parts might be easier/quicker to find.
So depending on your situation, you might actually still prefer the big companies with business models to supply parts to repair shops only (Scubapro, Apeks, Aqualung), and rely on the grey market. For me it matters most that parts for my reg models are available in the future and I have many part sources available over a wide geographic area.